1. Field of the Invention
The present invention relates to a tightening tool such as an electric screwdriver used for screw-tightening operation and more particularly, to a tightening tool having a clutch which appropriately provides not only for normal rotation but for reverse rotation.
2. Description of the Related Art
An example of a known electric screwdriver is disclosed in Japanese patent publication No. 3-5952, in which a clutch is used to connect a tool bit and a driving motor for transmitting the rotating torque. According to this technique, when the tightening tool or screw is tightened to a predetermined depth with respect to the workpiece, the clutch is promptly disengaged to stop transmission of the rotating torque according to the tightening depth.
According to the known screwdriver, the clutch is engaged when the user applies a pressing force on the body of the screwdriver, so that the torque of the driving motor is transmitted to the tool bit. Further, the clutch is disengaged in relation to the tightening depth of the screw. Therefore, when a pressing force of the user is not applied on the body, it may be difficult to keep the clutch in the engaged state in the screwdriver. As a result, screw-loosing operation by rotating the driving motor in a reverse direction may be basically impossible. In this respect, further improvement is required.